The present invention relates to oral care compositions, and more particularly, to oral care compositions for removing tooth stains.
Within the past decade, there has been an increase in interests for oral care products which can effectively improve the appearance of teeth, and more particularly, in oral care products which can remove tooth stains and whiten teeth. In general, tooth staining results from accumulated interactions of tooth components, such as, enamel, dentin, proteinaceous acquired pellicle, plaque, and tartar with external chromogens (e.g., chromogen-containing foodstuffs, beverages, tobacco, etc.) and internal chromogens (e.g., tetracycline, blood, etc.). The ability of each of the above tooth components to absorb and retain the external and/or internal chromogens is dependent upon the chemical and physical nature of both the tooth component and the associated chromogen.
In response to the interests in oral care products which can effectively improve the appearance of teeth, oral care companies have offered a variety of approaches to improving the appearance of teeth, including dentist-supervised in-office procedures, such as the use of high concentrations of peroxide and/or lasers, dentist-supervised take-home products, such as peroxide-containing gels and pastes administered to the patient in a custom made dental tray, and a multitude of over-the-counter (OTC) gel, paste, rinse, and spray products. Currently, the safety and/or effectiveness of over-the-counter gels and pastes which contain peroxides (often formulated at an acidic pH to improve stability) or other oxidizing agents intended to whiten teeth is still being debated, regardless of the manner in which the gels or pastes are being administered, for instance, by way of a dental tray or toothbrushing.
The removal of tooth stains may also be accomplished by utilizing an abrasive dentifrice or prophylaxis paste or gel to scrape off, for instance, a film of proteinaceous acquired pellicle and its associated chromogens through toothbrushing and/or dental prophylaxis. In general, the higher the level of abrasivity of a composition, the greater the extent to which the stained acquired pellicle may be removed. Highly abrasive compositions, however, have been known to remove layers of mineralized tissue from tooth enamel and dentin, in addition to the layer of acquired pellicle. As a result, both consumers and dental practitioners have expressed concerns over the possibility of damage to the enamel and dentin from highly abrasive toothpastes and gels.
A number of oral care compositions have been developed to address the above concerns. These compositions, however, have not always provided satisfying results. Specifically, when using pastes or gels, in order to obtain a visible difference in tooth whitening, those compositions which contain a relatively low level of oxidizing agents and/or acidic pH, may still employ highly abrasive materials. As the use of highly abrasive materials can damage the tooth enamel, those compositions may not always be used on a daily basis. For those oral care compositions which contain a relatively low level of abrasive materials, and for those compositions which contain a relatively low level of oxidizing agents, as well as a low level of abrasive materials, the degree to which a visible difference in tooth whiteness is noticeable has been disappointing.
It would thus be desirable to provide an effective composition for removing tooth stains without the use of oxidizing agents and/or an unduly high amount of highly abrasive components, so that the composition may be used on a daily basis without concern for damage to the oral mucosa, tooth enamel or dentin.
The present invention, in a preferred embodiment, is directed to removing tooth stains caused by the binding of chromogenic substances (referred to below as xe2x80x9ctanninsxe2x80x9d or xe2x80x9cphenolic compoundsxe2x80x9d)to the proteinaceous acquired pellicle on the tooth.
To remove such tooth stains, the present invention provides, in one embodiment, a novel oral care composition which includes (i) a destabilizing agent to disassociate and solubilize the chromogen from the layer of proteinaceous acquired pellicle, and (ii) a complexing agent having affinity for the disassociated chromogen to prevent its reassociation with the layer of proteinaceous acquired pellicle. The oral care composition of the present invention is preferably formulated to provide an oral pH equal to or above a pH for destabilizing the chromogen from its bond to the proteinaceous acquired pellicle, but less than a pH which can destabilize the chromogen from its bond to the complexing agent. In a preferred embodiment, the oral pH to be achieved by the composition is between approximately 7.0 and approximately 10.5. The composition may be in the form of a dentifrice, mouthrinse, chewing gum, or any other oral care delivery system providing sufficient oral contact time to permit destabilization of the bond between the chromogen and proteinaceous acquired pellicle and to allow for the complexing of the phenolic compound with the complexing agent.
In another embodiment, the present invention provides a process for manufacturing an oral care composition for removing tooth stains. The process includes first providing a water-soluble alkaline compound capable of disassociating a chromogen from a layer of proteinaceous acquired pellicle and obtaining a polymeric substance having affinity for the disassociated chromogen to prevent the chromogen from reassociating with the pellicle. A mixture of the polymeric substance and the alkaline compound is then created, so that when in use, an oral pH that is at least equal to a pH for destabilizing the chromogen from its bond to the proteinaceous pellicle, but less than a pH which can destabilize the chromogen from its bond to the polymeric substance. Once the mixture is created, the oral care composition is formulated from the mixture.
In a further embodiment of the invention, a method is provided for removing tooth stains. The method includes the steps of disassociating a chromogen from a layer of proteinaceous acquired pellicle on a tooth surface, and forming a complex between the disassociated chromogen and a polymeric substance having affinity for the chromogen to prevent reassociation of the chromogen with the proteinaceous acquired pellicle. In one embodiment of the method of the present invention, a composition may be provided which can disassociate the chromogen from the layer of acquired pellicle and which can form a complex between the chromogen and a polymeric substance.
The term xe2x80x9cacquired pelliclexe2x80x9d or xe2x80x9cproteinaceous acquired pelliclexe2x80x9d refers to a non-mineralized protein film, which tends to form when saliva contacts a clean tooth surface.
The term xe2x80x9ctanninxe2x80x9d refers to chromogenic substances and encompasses compounds known as phenolics which form tooth stains when complexed with the acquired pellicle on a surface of a tooth.
xe2x80x9cPhenolic compoundxe2x80x9d, as used hereinafter, refers to a compound having one or more benzene rings with at least one hydroxyl group attached directly to a benzene ring. Examples of phenolic compounds in foods and beverages include phenolic acids, coumarins, flavonoids, and polyphenolics.
Generally, after a tooth surface has been aggressively cleaned, such as that occurring during a dental prophylaxis with a pumice paste, the negatively-charged enamel surface on the tooth is exposed and is almost immediately contacted by saliva. Saliva contains components such as calcium ions and proline-rich proteins (PRP), which readily interact with amino acid side chains on the newly exposed negatively-charged enamel surface to form a proteinaceous film. This proteinaceous film tends to resist solubilization, even in highly acidic media, and may not dislodge, even by the constant salivary flow through the oral cavity. The strong interactions between the calcium ions and the amino acid side chains of the proteinaceous film, in addition to interaction with the inorganic hydroxyapatite component of enamel on the tooth surface may contribute to the film""s resistance to solubilization. Further accumulation of organic material from saliva, bacteria, gingival crevicular fluid, blood and other exogenous materials including food, dental materials, and oral hygiene products on the film can lead to the formation of the acquired pellicle.
Once formed, the proteinaceous acquired pellicle acts as a point of attachment for plaque-forming bacteria, which can lead to the development of a mature plaque matrix and, upon mineralization, to tartar. In addition, the proteinaceous acquired pellicle is highly interactive with dietary substances collectively known as tannins. Tannins, as indicated above, includes phenolic compounds, which when interact with proteins, such as the proteinaceous acquired pellicle, forms substantially insoluble complexes. (This complex will be hereinafter referred to as a xe2x80x9ctannin-protein complexxe2x80x9d). The formation or precipitation of the tannin-protein complex can subsequently lead to the formation of tooth stains. These tooth stains can be particularly difficult to remove because of the strength of the interaction between the tannin and the proteinaceous acquired pellicle. It should noted that the interaction of tannins, including phenolic compounds, with proteins to form insoluble complexes is well known and well described in the art.
To remove or enhance the removal of tooth stains, the present invention provides, in a preferred embodiment, an alkaline destabilizing agent to disassociate chromogenic tannin from the proteinaceous acquired pellicle, and a polymeric complexing agent having affinity for the disassociated chromogenic tannin to prevent reassociation of such chromogenic tannin with the proteinaceous acquired pellicle.
In one embodiment of the invention, the destabilizing agent may be a water-soluble alkaline compound. The alkaline compound preferably has a relatively low level of toxicity, so that it may be safely used to formulate an oral care composition. The preferred alkaline compound may be selected from the group consisting of alkali metals of an inorganic anion, ammonium salts of an inorganic anion, alkaline metals of an organic anion, ammonium salts of an organic anion, and combinations thereof. Examples of an inorganic anion are phosphate, polyphosphate, hydroxide, carbonate, bicarbonate, and borate. Examples of an organic anion are acetate, citrate, and lactate.
The complexing agent, on the other hand, may be a polymer that is capable of strongly interacting with the phenolic moieties of tannin, so that an insoluble complex between tannin and the complexing agent is formed. Particularly, the complexing agent of the present invention preferably has a higher affinity for the soluble tannin disassociated from the proteinaceous acquired pellicle, so that such tannin does not reassociate itself with the proteinaceous acquired pellicle.
In a preferred embodiment, polymers and copolymers (hereinafter referred to collectively as xe2x80x9c(co)polymersxe2x80x9d)of vinyl pyrrolidone, such as poly (vinyl pyrrolidone) and poly (vinyl pyrrolidone-co-vinyl acetate) are useful as a complexing agent. These (co)polymers have a molecular weight ranging up to about 60,000 Daltons, as determined by high-performance gel permeation chromatography, are water soluble, and tend to have a low toxicity level. As such, they are suitable for inclusion in the formation of the oral care composition of the present invention. Molecular weight may also be expressed in terms of an intrinsic viscosity, or K-value. The (co)polymers of vinyl pyrrolidone may, therefore, have a K-value ranging up to about 30. K-values are typically included in commercial specification of a particular (co)polymer, for instance, Kollidon 25 (k-value 25), a material manufactured by BASF Corporation. It should be appreciated that the vinyl pyrrolidone (co)polymers of the present invention, when included in an oral care composition at a concentration sufficiently high to effectively complex with a polyphenolic compound (i.e., tannin) disassociated from the proteinaceous acquired pellicle, do not appreciably contribute to the viscosity of the oral care composition.
(Co)polymers of ethylene oxide, such as polyethylene glycol, may also be used as a complexing agent for tannin which has disassociated from the acquired pellicle. In a preferred embodiment, polyethylene glycol has a molecular weight between about 2,000 Daltons and about 10,000 Daltons. At this molecular weight, similar to the (co)polymers of vinyl pyrrolidone, polyethylene glycol does not contribute significantly to the viscosity of the oral care composition. Polyethylene glycol is also low in oral toxicity, and is therefore suitable for use as a complexing agent in the oral care composition of the present invention.
The polymers and copolymers disclosed above are suitable as complexing agents because it is believed that each forms a complex with a solubilized tannin or polyphenolic substance disassociated from the proteinaceous acquired much more readily than the recomplexing of the such tannin or polyphenolic substance to the acquired pellicle. Although not wishing to be bound by any one particular theory, it is believed that the complexing polymers and copolymers, with a relatively high affinity for disassociated and solubilized tannin when compared to the acquired pellicle, act as anti-redeposition agents by scavenging and binding the such tannin, thereby preventing recomplexing of the tannin with the proteinaceous acquired pellicle.
In order to maintain a high affinity for the solubilized tannin disassociated from the acquired pellicle, the oral care composition of the present invention is formulated so that during use, a specific oral pH is achieved. Such pH is preferably substantially equal to or above a pH for destabilizing the tannin-protein complex, so that tannin may disassociate from the proteinaceous acquired pellicle, but less than a pH for destabilizing the complex between the tannin and a complexing agent. It has been found that an oral care composition formulated to achieve an oral pH of at least 7.0 is capable of providing the desired effect. An oral pH in a range of from between 7.0 and 10.5 is preferred.
The composition, of course, may contain other components typically found in oral care compositions, including flavoring agents and detergents/surfactants, examples of which include but are not limited to, sodium lauryl sulfate and sodium methyl cocoyl taurate. When a surfactant is used the concentration should be limited to that suitable for use within the cavity. A concentration of less than 5% by weight is preferred.
The delivery system for use with the composition of the present invention preferably includes any oral care delivery system with a sufficient contact time in the oral cavity to destabilize the staining tannin-protein complex. Examples of preferred delivery systems include toothpastes, mouthwashes, chewing gums, treatment gels, and others systems having utility in the application of the present composition. It should be noted, that immediately upon destabilizing the staining tannin-protein complex, the complexing polymer or copolymer will bind the soluble tannin, thus preventing it from recomplexing with proteinaceous acquired pellicle and restaining the tooth.
The following examples serve to illustrate a number of oral care compositions, in the form of toothpastes, which are useful in practicing the embodiments of the present invention. The examples, however, are not intended to limit the scope of the present invention.